Building the systems
Donaldson Co. began designing and making air filter systems 100 years ago, and now produces them for many heavy and medium trucks, according to Mike Anderson, director of product management for engine air business unit. Many filters now are smaller, he notes, because of the move to under-the-hood, very custom-designed systems.
To compensate, Donaldson offers more efficient and longer-lasting elements.
“Buyers can spec a pre-cleaner,” Anderson says. “The greatest challenge is to get air cleaners small enough and still meet the requirements. We have seen air flow increases along with demands for greater life. It's both efficiency and package size.”
Spinning of the air by pre-cleaners takes out larger particles and moisture, but there has to be a place for the moisture to go, Anderson says. In Europe, water separators are used; they're similar in design but have less restriction than U.S.-style pre-cleaners. The Technology & Maintenance Council of ATA suggests spec'ing a water separator to keep moisture out of the element and the engine.
Servicing remains a concern. “A lot of the systems continue to ingest water,” says Paul Bandoly, manager of technical service and customer training at Wix Filters. “So we've got to be cognizant of that — water ingestion and service life, because people are stretching service intervals way out.
So restriction gauges and air filter monitors have become more prevalent.” He believes they are as important on diesel pickups as on Class 8 trucks and tractors.
In addition, he says, owners should pay a lot more attention to the air induction systems, “There are lots of different kinds of clamping, lots of plastics, lots of modular stuff. Those things can become damaged and warped. So you've got to inspect the air induction system, from front to rear, and it's more critical than it ever was before. Clamps holding two molded devices together — they can change and loosen, and air can get in and bypass the filtration system.”
For many years, a common thing to secure the air filter was the wing nut and bolt, according to Bandoly. “Now you see the radial-seal air filter. If the filter's bent in any way, it won't fit into the housing properly and you'll get air bypassing the filter.”
How you handle the filter is important. “Don't buy one, throw it in the bed of your pickup and then throw something on top of it,” he says. Radial-sealing is good because it takes away the variability of tightness, but if the clamps are loose or ineffective, they will fail to seal properly.
Housings can get damaged; things get bumped and cracked because things happen in the shop. Things can loosen, so they need to be checked so that they're still secure, says Bandoly. Components are made to tolerate the underhood heat, but things can happen. “Now you're seeing air-induction sensors, mass air-flow sensors, and others that measure it, so air has to be cleaned at the high level of efficiency as it has been for years,” Bandoly says. “Some medium-duty diesels have programming that if they sense results less than what they expect, the Check Engine light can come on and they can go into limp mode.”
Don't dust the engine
Donaldson, which makes filter housings for OEMs and says it invented the radial seal 30 years ago, publishes posters showing mechanics the correct ways to open and reseal housings. It also has posted numerous video demonstrations on YouTube, which show steps to take to avoid dust damage.
“Dusting” a diesel begins when a careless mechanic yanks out an element and lets accumulated dirt fall further into the intake piping.
Upon startup, the engine sucks in the dirt, which damages the tur-bocharger, pistons, cylinder walls, injectors and other parts. Instead, the mechanic should carefully withdraw the element while using an oily rag to wipe dirt away from the exposed inlet, then wipe out the canister before installing a new element.
Reading the air restriction gauge, which many trucks today have, is the only way to know if the element needs changing, experts say. Looking at the element indicates nothing for sure, and seeing dirt on the element is not necessarily a sign that its life is over.
All elements work better after some dirt has adhered to its surface. And now the system has been opened and the engine put in danger of dusting, and someone is guilty of “over-servicing,” as defined by Recommended Practice 301C, published by the Technology & Maintenance Council.
“Restriction is simply resistance to flow,” the RP says. “Anything that directs the movement of the air (inlet accessory, ducting, housing, connections, elbows, etc.) imposes some restriction on the flow of air.
Restriction is normal and engines are designed to work with it. How much varies by engine size and output. Manufacturers publish acceptable and maximum restriction rates, as measured in inches of water. Watch the gauge to know how much the element is loaded up with contaminants, and change the element when the gauge says so.
“Once you get up to about 15 inches of restriction, it's time to service it, for ours, anyway,” advised Dino Marutsos, heavy-duty technical sales manager for K&N. “Some people say they don't work, but a static gauge isn't supposed to move. A dash-mounted gauge moves, and you have to watch for the highest restriction.”
Restriction gauges are properly read after the engine has worked at maximum output for a specified time, such as climbing an upgrade. At 15 inches, most dry elements are about 90% of capacity and servicing should be scheduled, the TMC recommended practice says.
Usually this means taking out the old dry element and replacing it with a new one. Some suppliers make washable filters that can be reused. One is K&N, best known for its low-restriction, high-performance elements for cars, light trucks and motorcycles. But its heavy truck filter elements, available since 2010, are instead designed for long life, Marutsos says. They can be cleaned in water or with low-pressure compressed air.
Filters and elements are tested according to standards set by the American Society for Testing Materials, which specifies the device and procedures for its use.
“The filter is placed in its own housing, and we shoot it with dirt and catch it in another area and measure it, explains Marutsos. “There's a larger test stand for the large, heavy-duty filters and a smaller one for the passenger car and motorcycle filters.”
If the goal is to take out 99.9% of contaminants, then the caught contaminants will add up to that percentage of the dirt thrown into the air stream. If not, it's back to the designer's computer screen.